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<td class="page-title-pattern-first-line " style="padding: 0px; border-collapse: collapse; font-family: Arial, sans-serif; font-size: 14px; padding-top: 10px"> <a href="https://hibernate.atlassian.net/browse/HHH" style="color: #3b73af; text-decoration: none">Hibernate ORM</a> / <a href="https://hibernate.atlassian.net/browse/HHH-10715" style="color: #3b73af; text-decoration: none"><img src="cid:jira-generated-image-avatar-82f59d1f-ee41-4bc5-9250-d149c015c2a2" height="16" width="16" border="0" align="absmiddle" alt="Improvement" style="vertical-align: text-bottom"></a> <a href="https://hibernate.atlassian.net/browse/HHH-10715" style="color: #3b73af; text-decoration: none">HHH-10715</a> </td>
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<td style="vertical-align: top;; padding: 0px; border-collapse: collapse; padding-right: 5px; font-size: 20px; line-height: 30px; mso-line-height-rule: exactly" class="page-title-pattern-header-container"> <span class="page-title-pattern-header" style="font-family: Arial, sans-serif; padding: 0; font-size: 20px; line-height: 30px; mso-text-raise: 2px; mso-line-height-rule: exactly; vertical-align: middle"> <a href="https://hibernate.atlassian.net/browse/HHH-10715" style="color: #3b73af; text-decoration: none">We should try to reduce the static field usage only when this is absolutely necessary</a> </span> </td>
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<th style="color: #707070; font: normal 14px/20px Arial, sans-serif; text-align: left; vertical-align: top; padding: 2px 0">Issue Type:</th>
<td class="has-icon" style="padding: 0px; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> <img src="cid:jira-generated-image-avatar-82f59d1f-ee41-4bc5-9250-d149c015c2a2" height="16" width="16" border="0" align="absmiddle" alt="Improvement" style="vertical-align: text-bottom"> Improvement </td>
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<th style="color: #707070; font: normal 14px/20px Arial, sans-serif; text-align: left; vertical-align: top; padding: 2px 0">Affects Versions:</th>
<td style="padding: 0px; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> 5.1.0 </td>
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<td style="padding: 0px; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> Unassigned </td>
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<th style="color: #707070; font: normal 14px/20px Arial, sans-serif; text-align: left; vertical-align: top; padding: 2px 0">Components:</th>
<td style="padding: 0px; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> hibernate-core </td>
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<th style="color: #707070; font: normal 14px/20px Arial, sans-serif; text-align: left; vertical-align: top; padding: 2px 0">Created:</th>
<td style="padding: 0px; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> 28/Apr/2016 04:03 AM </td>
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<td class="has-icon" style="padding: 0px; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> <img src="cid:jira-generated-image-static-major-d3258d46-806e-4f7d-9fc7-946299dfed14" height="16" width="16" border="0" align="absmiddle" alt="Major" style="vertical-align: text-bottom"> Major </td>
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<th style="color: #707070; font: normal 14px/20px Arial, sans-serif; text-align: left; vertical-align: top; padding: 2px 0">Reporter:</th>
<td style="padding: 0px; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> <a class="user-hover" rel="mih_vlad" id="email_mih_vlad" href="https://hibernate.atlassian.net/secure/ViewProfile.jspa?name=mih_vlad" style="color:#6c797f;; color: #3b73af; text-decoration: none">Vlad Mihalcea</a> </td>
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<td class="text-paragraph-pattern-container mobile-resize-text " style="padding: 0px; border-collapse: collapse; padding: 0 0 10px 0"> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0 0; margin-top: 0">As indicated by <a href="https://github.com/hibernate/hibernate-orm/pull/1198/files#diff-9f3d2f3cd0828afe20be0db68694f7a0L151" class="external-link" rel="nofollow" style="color: #3b73af; text-decoration: none">this PR</a>, there are some places where static fields are being used, which can cause some problems if we try to spawn several <tt>SessionFactory</tt> instances in the same <tt>ClassLoader</tt> (like when using Spring).</p> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0 0">Sanne has provided a very good summary on this topic:</p>
<blockquote style="margin: 10px 0 0 0; border-left: 1px solid #cccccc; color: #707070; margin-left: 19px; padding: 10px 20px">
<p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0 0; margin-top: 0">There are several components which can safely use static fields, of<br> course as you say only if their state is not affected by which<br> SessionFactory is using them.</p>
<p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0 0">So I would agree on treating those with care: it should always be a<br> warning sign during code reviews and warrant an in-depth check, but<br> ultimately it's a reasonable way to save some resources (both CPU and<br> memory) - especially when the same JVM runs multiple SessionFactory<br> instances.<br> Sure, savings might be small but when the component is clearly<br> stateless: why not.</p>
<p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0 0">I would assume this is a technical detail which we can handle without<br> needing to make a blanket statement.</p>
<p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0 0">+1 to avoid such tricks when it's not trivial to assert its safety,<br> yet there are valid use cases.</p>
<p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0 0">Looking at the specific case:<br> the usage of "private static Method memberMethod;" <span class="error">[1]</span> seems dodgy indeed.<br> Synchronization is clearly not the best solution, as it would create a<br> contention point were there's no need to create one. It would even<br> contend across multiple SessionFactory instances which is worse than<br> usual <img class="emoticon" src="cid:jira-generated-image-static-smile-d3d50428-fbdf-47a6-ac86-5aa3514b7222" height="16" width="16" align="absmiddle" alt="" border="0"></p>
<p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0 0">Indeed the code is "racy" as different threads might need to repeat<br> the effort of finding the reference to "memberMethod", it would have<br> been better to make the field "volatile" to ensure different threads<br> would see it;<br> yet the code is not functionally incorrect as any thread invoking that<br> method will behave the same, and retrieve the right value.</p>
<p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0 0">Better yet than volatile, make the "memberMethod" field Final, have it<br> initialized statically and move it to the top.. not sure why there are<br> fields hiding in the mid of a class <img class="emoticon" src="cid:jira-generated-image-static-smile-d3d50428-fbdf-47a6-ac86-5aa3514b7222" height="16" width="16" align="absmiddle" alt="" border="0"></p>
<p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0 0">BTW this is a good example of sane usage of static (final) fields: it<br> doesn't matter which SessionFactory is running or how it's configured,<br> but it's a good thing that different SessionFactory instances won't<br> have to repeat the initialization of that field over and over.</p>
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